During production, substrates are often handled by robotic arms that are equipped with specialized tools, or “end effectors,” that are adapted for lifting and moving the substrates. Since substrates can reach high temperatures during processing (e.g., >500° C.), end effectors generally are made from materials that exhibit good thermal stability and wear resistance at high temperatures. Examples of such materials include alumina, zirconia, silicon nitride, silicon carbide, and other ceramics.
Conventional high-temperature end effectors are often made entirely from ceramic. One problem associated with such a construction is that when the substrate-contacting portions of such end effectors become excessively worn or contaminated from use, the entire end effector must be replaced. Such replacement can be expensive as well as wasteful, since the non-material-contacting portions of the end effector may exhibit little or no wear at the time of replacement.
One approach to this problem has been to use composite end effectors, which include substrate-contacting portions that are removably attached to non-material-contacting portions. In some cases, several small contact pads formed of ceramic material are removably attached to the end effector body, which can be made of metal. During use, only the ceramic contact pads contact with hot substrates and thus experience wear over time. When the contact pads become worn or contaminated they are removed and replaced with new contact pads. The end effector body itself needn't be replaced and is thereby preserved.
Although composite end effectors offer several advantages relative to one-piece end effectors, still they have shortcomings. For example, the low thermal expansion and low tensile strength properties of ceramics relative to metals makes it difficult to achieve a secure, rigid connection between the two materials as is required for the construction of a composite end effector. Prior designs have employed threaded connections, press-fit pads, and retaining rings. Each of these fastening arrangements, however, exhibits particular deficiencies. For example, threaded fasteners can impart stresses on ceramic contact pads during thermal cycling, which may result in cracking of the contact pads. Threaded fasteners may also become loose over time due to vibrations and/or thermal cycling. Press-fit pads typically cannot be made from ceramic are difficult to remove when replacement become necessary. Retaining rings that clamp pads to an end effector can generate particles due to relative motion. Such particles can rain down on other silicon wafers which can be detrimental to their quality. Thus, there is a need for an improved design for a replaceable contact pad that overcomes the deficiencies associated with prior designs.